''Viatkogorgon'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

gorgonopsian Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of Saber-toothed predator, sabre-toothed therapsids from the Middle Permian, Middle to the Upper Permian, roughly between 270 and 252 million years ago. ...

(a type of therapsid, the group that includes modern

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s) that lived during the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

period in what is now Russia. The first

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

was found at the

Kotelnich Kotelnich (; ) is a river port town in Kirov Oblast, Russia, located on the right bank of the Vyatka River near its confluence with the Moloma, along the route of the Trans-Siberian Railway, southwest of Kirov. Population: History The loca ...

locality near the

Vyatka River The Vyatka is a river in Kirov Oblast and Tatarstan in Russia. It is a right tributary of the Kama.holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of the new genus and

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

''V. ivachnenkoi'' in 1999. The generic name refers to the river and the related genus ''

Gorgonops ''Gorgonops'' (from 'Gorgon' and 'eye, face', literally 'Gorgon eye' or 'Gorgon face') is an extinct genus of gorgonopsian therapsid, of which it is the type genus. ''Gorgonops'' lived during the Late Permian (Wuchiapingian), about 260–254 ...

''—the

gorgon The Gorgons ( ; ), in Greek mythology, are three monstrous sisters, Stheno, Euryale, and Medusa, said to be the daughters of Phorcys and Ceto. They lived near their sisters the Graeae, and were able to turn anyone who looked at them to sto ...

s of

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

are often referenced in the names of the group. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honors the paleontologist Mikhail F. Ivakhnenko. The holotype skeleton is one of the most complete gorgonopsian specimens known and includes rarely preserved elements such as

gastralia Gastralia (: gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these reptil ...

(abdominal ribs) and a

sclerotic ring The scleral ring or sclerotic ring is a hardened ring of plates, often derived from bone, that is found in the eyes of many animals in several groups of vertebrates. Some species of mammals, amphibians, and crocodilians lack scleral rings. The rin ...

(a bony ring inside the eye). A larger, but poorly preserved specimen has also been assigned to the species. The holotype specimen is about long, including the long skull, making ''Viatkogorgon'' a relatively small gorgonopsian. The assigned specimen is larger, with a long skull, and the holotype may have been young. As a gorgonopsian, it would have been skeletally robust with a somewhat dog-like stance, though with outwards-turned elbows. The

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, Rostrum (anatomy), rostrum, beak or proboscis. The wet furless surface around the nostrils of the n ...

was high, and the teeth were generally recurved (curved backward), pointed, and

serrated Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied pr ...

. The canines (the saber teeth) were much larger than the

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s at the front and postcanines behind but relatively small for a gorgonopsian. ''Viatkogorgon'' was characterized by its unusually large eye socket and sclerotic ring. It was distinct from other gorgonopsians in that the lower end of the

postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...

was narrow, and it had a very large sulcus (or furrow) at the back of the skull on each side. Since gorgonopsians have been described mainly from skulls, it is uncertain how widespread the

postcranial The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

features of ''Viatkogorgon'' were in other members of the group. The skeleton of ''Viatkogorgon'' was unusual in having gastralia, in that the tail was differentiated with a front and hind part, with the former less flexible, and in that some of the foot bones and its digits were reduced in size and interconnected. Gorgonopsians were a group of

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

stem mammals with saber teeth that disappeared at the end of the Permian.

Phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

has found ''Viatkogorgon'' to be one of the earliest-diverging gorgonopsians, after ''

Nochnitsa ''Nochnitsa'' is an extinct genus of gorgonopsian therapsids who lived during an uncertain stage of the Permian in what is now European Russia. Only one species is known, ''N. geminidens'', described in 2018 from a single specimen including a com ...

'', also from Kotelnich. All other gorgonopsians appear to belong to two, later-diverging Russian and African groups. ''Viatkogorgon''s proportionally large sclerotic ring suggests

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

habits. Gorgonopsians would have been relatively fast

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

, killing their prey by delivering slashing bites with their saber teeth. The skeleton of ''Viatkogorgon'' had features such as a

vertebral column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmente ...

with increased vertical curvature, including the hind part of the tail, and restricted mobility of some digits of the feet, likened to a

flipper Flipper may refer to: Common meanings *Flipper (anatomy), a forelimb of an aquatic animal, useful for steering and/or propulsion in water *Swimfins, footwear that boosts human swimming efficiency, also known as flippers * Flipper (cricket), a typ ...

-like structure indicating it may have been a relatively good swimmer. The age of the Vanyushonki Member of the Kotelnich succession, from which ''Viatkogorgon'' is known, is not determined but is thought to date to either the

late Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

middle Permian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

epoch.

Discovery

In 1999, the

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Leonid P. Tatarinov described and named a new genus and species of gorgonopsian (a group of stem-mammals with saber teeth that lived during the Permian period), ''Viatkogorgon ivakhnenkoi''. The holotype specimen (cataloged as PIN 2212/61 in the

Paleontological Institute of the Russian Academy of Sciences The Paleontological Institute, Russian Academy of Sciences (PIN; ) in Moscow is among a paleontological institute. An affiliate of the Russian Academy of Sciences, it includes collections from all over the former Soviet Union, as well as from other ...

in Moscow), on which the scientific name is based, was found in 1992 at the

locality of

Kotelnichsky District Kotelnichsky District () is an administrativeLaw #387-ZO and municipalLaw #284-ZO district (raion), one of the thirty-nine in Kirov Oblast, Russia. It is located in the west of the oblast. The area of the district is . Its administrative center is ...

, in Russia's

Kirov Oblast Kirov Oblast ( rus, Кировская область, p=ˈkʲirəfskəjə ˈobləsʲtʲ) is a federal subject of Russia (an oblast) located in Eastern Europe. Its administrative center is the city of Kirov. As of the 2010 census, the population ...

. The Kotelnich locality contains a series of Permian exposures on the banks of the

Vyatka River The Vyatka is a river in Kirov Oblast and Tatarstan in Russia. It is a right tributary of the Kama. The generic name ''Viatkogorgon'' refers to the Vyatka River, and to ''Gorgonops'', the name of a related genus. The name "

", referring to the monstrous

hag A hag is a wizened old woman, or a kind of fairy, witch, or goddess having the appearance of such a woman, often found in folklore and children's tales such as "Hansel and Gretel". Hags are often seen as malevolent, but may also be one of t ...

s of

, is often used in the generic names of gorgonopsians. The specific name ''ivakhnenkoi'' honors the paleontologist Mikhail F. Ivakhnenko. The specific name was spelled ''V. ivachnenkovi'' in a 2001 article by the paleontologists Elena G. Kordikova and Albert J. Khlyupin, a spelling which Tatarinov modified slightly in 2004 as ''V. ivachnenkoi'', while some other researchers have continued using the original spelling. Russian gorgonopsid discoveries began in the 1890s with notable finds like ''

Inostrancevia ''Inostrancevia'' is an extinction, extinct genus of large carnivorous therapsids which lived during the Late Permian in what is now European Russia and Southern Africa. The first-known fossils of this gorgonopsian were discovered in the context ...

'', one of the largest members of the group. There were fewer finds during the 20th century, with ''Viatkogorgon'' being the first recognized gorgonopsian from Russia, the only place outside Africa where the group is definitely known, since 1974. The holotype skeleton is one of the most complete gorgonopsian specimens known (a 2023 study called it the most complete), and preserves almost the entire

postcranial skeleton The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

(the rest of the skeleton apart from the skull). This includes elements rarely preserved intact in therapsids (the group in which gorgonopsians belong), such as the gastralia (or abdominal ribs, a feature found among

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s, for example). The skull is relatively poorly preserved in comparison, with the left side and the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...

badly broken. The skull roof is reconstructed in plaster, except for the snout tip and left

postorbital bone The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ...

(the bone that formed the hind border of the

eye socket In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is ...

). Overall, the skull is also compressed from side to side, which makes it narrower than it would have been in life when viewed from above. The right

(a bony ring inside the eye) is preserved, which is otherwise uncommonly preserved in

theriodont The theriodonts (clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, ...

(the sub-group of therapsids to which gorgonopsians belong) fossils. The proatlas,

atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

and

axis An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...

(the first bones of the vertebral column) are attached to the skull. Tatarinov only described the skull of ''Viatkogorgon'' in the 1999 article, wherein he also named the new scylacosaur genus '' Kotelcephalon'', because the article was restricted in volume, but he preliminarily described the postcranium in 2004. In 2018, the paleontologists Christian F. Kammerer and Vladimir Masyutin redescribed the skull of ''Viatkogorgon'' and stated that a detailed description of the postcranium would greatly improve understanding of the skeletal anatomy of gorgonopsian, but noted it was unavailable for study during their research, as it was part of a traveling exhibition. They also named the new gorgonopsian ''

'' from Kotelnich in the article. In 2002, Ivakhnenko reported an additional, larger ''Viatkogorgon'' specimen (cataloged as PIN 4678/5), which is very poorly preserved.

Description

The almost complete ''Viatkogorgon'' holotype specimen is about long, including the skull. The skull is , the preserved part of the tail is approximately , the forelimb is approximately , and the hindlimb is more than . It was relatively small for a gorgonopsian; for comparison, ''Inostrancevia'' and ''

Rubidgea ''Rubidgea'' is a genus of gorgonopsian from the upper Permian of South Africa and Tanzania, containing the species ''Rubidgea atrox''. The generic name ''Rubidgea'' is sometimes believed to be derived from the surname of renowned Karoo paleonto ...

'' measured at least in length. Ivakhnenko suggested in 2002 that the holotype specimen was possibly a young individual, based on it having a narrow

; the width of this bar widened with age in ''

Estemmenosuchus ''Estemmenosuchus'' (meaning "crowned crocodile" in Greek language, Greek) is an extinct genus of large, early omnivore, omnivorous therapsid. It is believed and interpreted to have lived during the middle part of the Middle Permian around 267 m ...

'', for example. For comparison, the skull of the larger assigned specimen is long, and its postorbital bar is wide, while that of the holotype is . The skull length was therefore increased 1.3-fold, and the width of the postorbital bar was increased by a factor of 1.6. Gorgonopsians were skeletally robust, yet long-limbed for therapsids, with a somewhat dog-like stance, though with outwards-turned elbows. It is unknown whether non-

mammaliaform Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during the Late Triassic. It is defined a ...

therapsids such as gorgonopsians were covered in hair or not.

Skull

The snout of ''Viatkogorgon'' was high and narrow, though much of the skull's narrowness was due to sideways compression of the fossil. The

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

(the frontmost bone of the upper jaw) was little exposed on the side surface of the snout, as in ''Nochnitsa''. The internarial bar (which divided the nostrils) curved slightly hindward in side view, so that the lower front margin of the snout was blunt rather than pointed. The upper tip of the premaxilla extended to the upper front edge of the bony nostril. Few of the upper

s (front teeth) are preserved intact in the holotype, but the partial tooth roots and

tooth sockets Dental alveoli (singular ''alveolus'') are sockets in the jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament. The lay term for dental alveoli is tooth sockets. A joint that connects the roots of the t ...

show it would have had five incisors on each side, as is typical for gorgonopsians. The upper incisors were weakly curved and spatulate (spoon-shaped), with clear

serration Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied pr ...

s towards their tips. It is uncertain if they decreased in size further back in the tooth-row, because the holotype's only two intact incisors are the same tooth of each side (I5). In general, the teeth were pointed, flattened on the outer side, and somewhat convex on the inner side, and the serrated area of each tooth was displaced towards the outer edge of the crowns. The septomaxilla (a small bone between the

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

and the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

, the main bone of the upper jaw) had a shorter side facing

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...

than ''Nochnitsa''. Viatkogorgon skull

The maxilla was proportionally taller and shorter from front to back than in ''Nochnitsa'', and whereas the upper margin of the latter's maxilla was rounded, there was a broad process that extended hindward between the nasal and

lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...

(a bone that formed the front border of the eye socket) in ''Viatkogorgon''. The hindward directed process that formed the lower margin of the maxilla was shorter than in ''Nochnitsa'', not reaching the midpoint of the eye socket. The "step" by the

diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...

(gap) between the incisors and the

canine Canine may refer to: Zoology and anatomy * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...

(the saber-tooth) was deeper than in ''Nochnitsa'', and the part of the maxilla that bore the canine was very convex, which gave the impression of a "flange" when seen in side view. The canine was relatively small for a gorgonopsian, as was the case in ''Nochnitsa'', and bore serrations on its hind edge. The tooth row behind the canine was short and consisted of four closely packed postcanines, which were recurved (curved backwards), unlike those of ''Nochnitsa''. The postcanines were substantially shorter than the incisors, a regular feature of gorgonopsians, and almost three times shorter than the canines. There was a weak margin above the postcanine tooth-row on the maxilla, to a larger extent than ''Nochnitsa'', but less than in the gorgonopsian '' Eriphostoma'' and rubidgeines. The nasal bone of ''Viatkogorgon'' was somewhat broader at the front (by the hind edge of the bony nostril) than in ''Nochnitsa''. The

prefrontal bone The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and ...

(at the forehead, above and in front of the eye) was proportionally shorter than in ''Nochnitsa'' and contributed less to the upper front margin of the eye socket, where the lacrimal bone formed a larger part instead. ''Viatkogorgon'' was characterized by its unusually large eye socket with its proportionally large sclerotic ring. The diameter of the eye socket was , while the outer diameter of the sclerotic ring was , and its inner diameter . The ring consisted of 15 ossicles (small bones also termed plates) which overlapped each other with no gaps, and the rims of the ring were regularly rounded. The

jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic bone, zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by spe ...

, which formed the lower border of the eye socket of ''Viatkogorgon'', formed a more extensive part of the side of the face than in ''Nochnitsa''. ''Viatkogorgon'' was distinct from all gorgonopsians except ''Nochnitsa'' in that the lower end of the postorbital bar (between the eye socket and the

temporal fenestra Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

opening behind the eye socket) was narrow, forming a straight rod when seen in side view. It was broader and lacked the curvature seen in the bar of ''Nochnitsa''. In other gorgonopsians, the lower end of the postorbital bar was expanded where it contacted the jugal bone, even if the rest of the upper length of this bar was narrow. The skull of ''Viatkogorgon'' was also distinct in having a very large sulcus (or furrow) on the

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...

on each side at the back of the skull, which extended onto a squamosal flange which impinged on the lower edge of the temporal fenestra. Apart from being much larger and expansive than the squamosal sulcus of ''Nochnitsa'', this feature had a distinct boundary and a flange that pointed back and down in both. Sauroctonus palate bosses and teeth

The palatal structure of ''Viatkogorgon'' was typical for gorgonopsians. It had teeth on the

palatine bone In anatomy, the palatine bones (; derived from the Latin ''palatum'') are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxilla, they comprise the hard palate. Stru ...

(bony palate) placed on stout

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...

s (also called bosses, with 15–18 teeth on each), which formed two rows that extended along the outer and inner edges of each tubercle. Each tooth row formed two lines, with the outer line being longer than the inner. The surface of the tubercle was weakly concave and smooth between the teeth. There were also tooth-bearing tubercles on the

pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates, behind the palatine bone In anatomy, the palatine bones (; derived from the Latin ''palatum'') are two irregular bones of the facial skeleton in many animal specie ...

behind the palatine bone, though less developed, and the teeth here (12–13 on each) were similar to those of '' Sauroctonus''. They were much smaller than the palatine teeth, covered the entire surface of the tubercles, and formed three rows. There were also teeth on the transverse processes of the pterygoid, which formed only one row mainly on the inner part, unlike in ''Sauroctonus''. Unlike the teeth on the tubercles, these teeth were strongly worn and probably not replaced in adults. The lower jaw of ''Viatkogorgon'' was typical for gorgonopsians, unlike that of ''Nochnitsa'', with a tall

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...

(the area where the two halves of the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

connected at the front) and distinct

mentum The term mentum can refer to several anatomical structures near the mouth of an animal: *The median plate of an insect's labium. *The protruding part of the human chin. *A certain thin projection of the soft parts of the animal, below the mouth, i ...

(or "chin"). The lower jaw was somewhat shorter than the upper jaw. The lower teeth are badly preserved in the holotype, but they appear to have been very similar to the upper; the single preserved incisor is recurved and spatulate, and the lower postcanine is weakly recurved, and both at least have serrations on their hind edges. The

dentary bone In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

(the tooth-bearing bone at the front of the lower jaw) was generally taller than that of ''Nochnitsa'', and its coronoid process (part of where the jaw connected to the skull) sloped more sharply, with a weakly concave hind edge, as is typical in gorgonopsians. The

articular bone The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two othe ...

(which formed the jaw-joint) was typical of gorgonopsians and had a downward protruding retroarticular process (a process at the back of the jaw where muscles attached).

Vertebrae and ribs

Since gorgonopsians have been described mainly from remains of their skulls, with scant known postcranial remains, it is uncertain how widespread the postcranial features of ''Viatkogorgon'' were in other members of the group. ''Viatkogorgon'' had seven

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

(of the neck), twenty or twenty-one

thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

(of the body in front of the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

, fifteen when excluding the five

lumbar vertebrae The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe t ...

, those between the ribcage and the pelvis), three

sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

(associated with the pelvis), and at least twenty

caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...

(of the tail). The structure of the atlas was similar to other gorgonopsians, and the other neck vertebrae were massive, particularly the axis. The axis had a relatively large intercentrum, a very large

neural spine Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

, which expanded from front to back, and a very high front side. The zygapophyses (the articular processes that connected adjacent vertebrae) were horizontal in the axis but became more vertical beginning by the third vertebra. The thoracic vertebrae of ''Viatkogorgon'' were somewhat shorter than the lumbar vertebrae, and their neural spines were moderately tall, with horizontal zygapophyses. The neural spines became somewhat taller beginning at the second third part of the thoracic region, and were vertical in side view, though in the hind part of this region they were inclined rearwards and their front edge became convex (showing the transition from thoracic to lumbar vertebrae). The front ten or eleven thoracic

ribs The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...

were very long and directed back and down. They were closely adjoined and attached at the front edge of the centrum by two closely positioned articular heads, as in the other ribs. The hindmost four or five thoracic rib pairs shortened gradually, transitioning into the lumbar ribs, whose articular heads got closer together. The

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

(breast bone) was long, shaped like a rectangular plate, and had three costal processes on each side, similar to ''

Aelurognathus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa and Zambia. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontol ...

''. The gastralia of ''Viatkogorgon'' formed an unusual, latticed frame of segmentally arranged narrow bars, located under the frontmost thoracic ribs. The bars were arranged in two layers at an angle to each other, with at least thirteen bars extended frontwards and down at the deeper layer. The four at the upper layer continued the thoracic vertebrae and extended hindward and down. The left bars overlay the lower ends of the right bars in some cases, and these elements were much thinner and denser spaced than ribs. No element connecting the right and left ribs has been identified. Viatkogorgon2DB

The lumbar region was slightly differentiated from the thoracic region in having shorter ribs. The first and second lumbar ribs curved slightly hindward, were directed almost to the sides in the third, and curved slightly forwards in the hindmost two vertebrae. The lumbar ribs appear to have been single headed, unlike the thoracic ribs. The lumbar vertebrae were massive, longer than the thoracic ones, and had horizontally positioned zygagophyses and somewhat thickened neural spines, whose front edges narrowed towards the top. The three frontmost lumbar vertebrae had horizontal diapophyses (processes which projected from the sides of the

neural arches Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

over the

neural canal In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, ...

of the vertebrae), while these turned in a vertical direction in the two hindmost ones, as seen in some other gorgonopsians. Of the three sacral vertebrae, only the hindmost two connected to the ilium of the pelvis by expanded ribs, the ends of which adjoined each other to form a common articular facet. The articular facet of the frontmost vertebra was isolated from the other two, and only connected with a shortened, rudimentary rib. The tail region of ''Viatkogorgon'' was clearly differentiated into a front and hind part, the front part consisting of five caudal vertebrae which together measured in length. The ribs were short and massive in this part of the tail region. The zygapophyses were unusually inclined upwards, with their hind edges raised in relation to their front edges. The position of the zygapophyses would have restricted sideways movement at the base of the tail. The zygapophyses of the fourth and fifth caudal vertebrae were less inclined. The ribs of two of the front caudal vertebrae were long, whereas they shortened abruptly so that the rib of the fifth vertebra was only long. All the ribs here were double-headed, and all the neural spines were relatively massive, though they abruptly decreased in length hindward. The hind part of the tail consisted of 15 vertebrae, which lacked caudal ribs. In at least four of these vertebrae, the zygapophyses were almost raised to the extent of those of the vertebrae that adjoined their front, while they were positioned almost horizontally towards the back. The neural spines here were low and narrow, and the space between the vertebrae had well-developed hypapophyses (processes that project down from the vertebrae) that did not taper. The hypapophyses were inclined hindward and adjoined two vertebrae at the front, and covered the hypapophyses hindward adjoining vertebrae from below.

Limbs and limb girdles

The scapula (shoulder blade) was long, nearly wide at the joint with the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

(upper arm bone), and its upper edge expanded to a width of . A relatively low crest extended along the hind edge of the bone's lower third, and slightly deviated at the front from the edge of the scapula. The

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

s (part of the

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...

in vertebrates other than mammals) were displaced somewhat upwards and closely adjoined the inner surface of the scapula, projecting from the front and back of that bone. The external

foramen In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, artery, ...

(opening) of the coracoid opened in front of the scapula. The internal foramen opened into an incisure between the procoracoid and the scapula, a position also seen only in ''Gorgonops'' among gorgonopsians. The humerus was shorter than the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

(thigh bone), and long respectively but much more massive. The deltopectoral crest (where muscles attached to the upper arm) of ''Viatkogorgon'' projected to about the same extent as in ''Sauroctonus'' but with a more poorly developed

greater trochanter The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system. It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Sta ...

(a site for muscle attachment). The humerus of ''Viatkogorgon'' was similar to that of ''Aelurognathus'', though with a more massive elbow joint, almost in diameter across. Russian tetrapod

The lower

epicondyle An epicondyle () is a rounded eminence on a bone that lies upon a condyle ('' epi-'', "upon" + ''condyle'', from a root meaning "knuckle" or "rounded articular area"). There are various epicondyles in the human skeleton The human skeleton is ...

s (the rounded parts at the end of a bone) of the humerus were very well-developed and projected far above the surfaces that articulated with the lower bones, with rough crests at the edges. The crest on the medial epicondyle (associated with the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

of the lower arm) was massive, and the crest of the lateral epicondyle (associated with the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

) was longer, 20% of the humerus' length but less massive. Most other gorgonopsians did not have as prominent and sculptured lateral epicondyles, except for one indeterminate specimen. There were two epicondylar foramina, one more extended and in a more upward position, the difference between the two being greater than in ''

Lycaenops ''Lycaenops'' ("wolf-face") is a genus of carnivorous therapsids. It lived during the Middle Permian to the early Late Permian, about 260 mya, in what is now South Africa. Description Like the modern-day wolves from which it took its name, '' ...

''. The strongly developed upper epicondyles made the humerus of ''Viatkogorgon'' s-shaped, while those of almost all other gorgonopsians were only slightly concave on one side. The lower arm was about long. The radius was narrower than the ulna but also flattened from top to bottom. The ulna was much more massive than the radius and had a well-developed ulnar process. The ulna was flattened from top to bottom, and its upper part had a roughened area bordered by crests, which marked where the

flexor muscles Anatomical terminology is a specialized system of terms used by anatomists, zoologists, and health professionals, such as doctors, surgeons, and pharmacists, to describe the structures and functions of the body. This terminology incorporates a ...

of the hand originated. ''Viatkogorgon''s hand was narrow and about long. The middle digits projected to a larger extent than the ones on the foot and had a typical gorgonopsian structure. ''Viatkogorgon'' was unusual in having two small additional centrale bones among the

carpal bones The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός ...

of the hands, while most other gorgonopsians had only one. The fifth digit of the hand was very specialized, and its structure was superficially like the human thumb, the first digit in the human hand. The other digits were more typical in appearance. The first digit had short bones, and the third digit was the longest, like other gorgonopsians, but its length exceeded the others to a larger extent. The

phalanx bones The phalanges (: phalanx ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. Struct ...

of the fourth digit were complex, their outer ends having a disk-like element that attached tightly with the main part of the phalanges, yet these were of the same length as the ordinary phalanges. The ilium of ''Viatkogorgon'' differed from that of ''Lycaenops'' in that its preacetabular part (the part in front of the

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

, the

hip joint In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint o ...

where the femur connected) was better developed with a pronounced muscular depression. This probably provided an area for attachment for the iliotibial muscle that connected with the lower leg. The upper margin of the ilium was raised far above where this bone articulated with the sacrum and had a longitudinal crest on the inner surface. This was separated from another crest by a fossa which, along with a broad depression, may have provided an area of attachment for part of the ilio-pubo-femoralis internus muscle. The pubic bone was thickened, rod-like, and directed forwards and down at an angle of about 45 degrees, resembling the pubic bones of

archosaurian Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistic sense of the t ...

reptiles (the group that includes crocodiles and dinosaurs). The acetabulum was very large and horizontally elongated, measuring over long and high. On the lower edge of this opening, a notch separated the

ischium The ischium (; : is ...

from the pubic bone. The femur was proportionally long, , 70% of the skull's length. It was more massive than that of ''Lycaenops'', and curved along its long axis, to the same extent as in ''Sauroctonus''. The head of the femur was round, about in diameter, directed inward at about a 30-degree angle, and its surface was well-built. The femoral head narrowed towards its back, and it likely entered the hind part of the acetabulum. The greater

trochanter A trochanter is a tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans have two, sometimes three, trochanters. Etymology The anatomical term ' ...

descended to about the femur's mid-length. Two long crests extended along the bone, above and below the front of the greater trochanter. The first was probably the inner trochanter, which was typically present in gorgonopsians, but the other has not been identified previously in the group. The lower leg was shorter than the femur, at most, and its surface sculpturing was more pronounced than in other gorgonopsians, resembling

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s. The

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

(lower leg bone) of ''Viatkogorgon'' had structures not identified in other gorgonopsians, such as a flattened surface on the preaxial epicondyle, and a crest at the upper half back of the bone that bordered a broad area. The

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

(lower leg bone) was more massive than those of other gorgonopsians and had a massive sculptured crest at its middle; this surface sculpturing diminished towards the lower end of the fibula, and the crest abruptly decreased in height, features not seen in other gorgonopsians. ''Viatkogorgon''s foot was long, and its general structure was similar to those of other gorgonopsians, though some features were notable. The proximal row of bones towards the heel consisted of only two bones as in mammals—a massive

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

and a fibulare. In the distal row at the front of the foot, the fourth and fifth tarsals were fused, as in other gorgonopsians, but the row of intermediate centralia in ''Viatkogorgon'' was unusually well-developed; gorgonopsians usually had only one centrale, whereas ''Viatkogorgon'' had an additional one. Another unusual feature was that the articular facets of the hindmost foot bones extended onto the front side of the fibula and tibia of the lower leg. The tarsus (the hindmost cluster of bones in the foot) was long, and the

metatarsal bones The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...

(those between the tarsus and the digits) ranged from , the first, to , the fourth. The foot's digits were short, the fourth being , a little longer than the third. The digits varied slightly in length, with the second and fifth digits being only slightly shorter than the third and fourth. The shortening of the metatarsals added to the impression that the digits were short. The first and fifth digits were somewhat hooked; the first was relatively short, about long. The phalangeal formula (the number and distribution of phalanx bones in the digits) of gorgonopsians was similar to that of mammals, while the study of ''Viatkogorgon'' indicates there was a reduction in phalanges (leading to phalanges becoming disk-like) combined with fusion of them. In the first digit of the foot, two phalanges were almost completely fused. In the third digit the second and third phalanges were shortened and fused. The fourth digit had three phalanges that were shortened, almost disk-like, and fused. Therefore, the phalangeal formula was 1-2, 3, 3-4, 3-5, 3. There was contact between the metatarsals towards the back of the foot, as well as contacts between some metatarsals and phalanges and contacts between the bases of the second and third digits.

Ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

s probably mediated the front contacts between the metatarsals and phalanges. The ungual phalanx (claw bone) of the fifth digit was notable in being hooked and somewhat lengthened.

Classification

Gorgonopsians were a group of carnivorous therapsids that included the

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

s of the late Permian. While they were abundant, they varied little in

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

. Though widespread in southern Africa during the Permian, they are poorly represented in the fossil record of the rest of the world, and only definitely known from Russia. Gorgonopsians were early synapsids, the group in which modern mammals belong; similar to reptiles in some respects, they are therefore considered stem-mammals (earlier inaccurately termed "mammal-like reptiles"). Gorgonopsians were the first group of predatory animals to develop saber teeth, long before true mammals and

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s evolved. This feature later

evolved independently Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

multiple times in different predatory mammal groups, such as

felids Felidae ( ) is the family of mammals in the order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant Felidae species exhibit the greatest diversity in fur patterns of all terrestria ...

and thylacosmilids. Gorgonopsians disappeared with the end-Permian mass extinction. In his 1999 description, Tatarinov found ''Viatkogorgon'' to belong in the gorgonopsian

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Sycosaurinae within the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Gorgonopsidae, based on features such as small size and the narrowness of the snout. This subfamily was not previously known from Russia. He also noted some similarities to members of the family Rubidgeidae. Ivakhnenko considered Sycosaurinae, including ''Viatkogorgon'', to be part of Rubidgeidae in 2002. In his 2004 description of the postcranial skeleton, Tatarinov cautioned that this provided little information about the

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

position of ''Viatkogorgon'' among gorgonopsians—some features being unique and others occurring in other members of the group. The lack of information resulted from only a few gorgonopsians having had their skeletons examined. Nevertheless, he found the structure of its feet similar to gorgonopsians such as ''

Arctognathus ''Arctognathus'' is an extinct genus of gorgonopsids that throve during the Late Permian in the Karoo basin of what is now South Africa. Discovery A carnivore, like all gorgonopsid, ''Arctognathus'' was given its name ("Bear jaw") in referen ...

'' and ''Aelurognathus''. In 2018, Kammerer and Masyutin stated that while the early evolution of Gorgonopsia is poorly understood, ''Viatkogorgon'' and ''Nochnitsa'' expand the knowledge of gorgonopsians from the middle Permian or earliest late Permian of

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

, the northern landmass of the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...

, consisting of what is now Eurasia and North America. In their

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

, ''Nochnitsa'' was found to be the

basalmost In phylogenetics, basal is the direction of the ''base'' (or root) of a rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to th ...

(earliest-diverging) gorgonopsian followed by ''Viatkogorgon'' (based on its lack of a lower expansion on its postorbital bar, a feature seen in later-diverging genera), these being outside a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

grouping all other gorgonopsians. That clade was again divided into two groups, one consisting of Russian and the other consisting of African gorgonopsians, based on shared skull features. The following

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing the position of ''Viatkogorgon'' within Gorgonopsia follows Kammerer and Rubidge, 2022: In contrast, previous analyses had not found gorgonopsians to be grouped geographically, with some studies placing Russian genera such as ''Inostrancevia'' in African families. Previously, it had not been suspected that different gorgonopsian groups were

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to different regions. Kammerer and Masyutin found it surprising since there were many Russo-African

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

relationships between other therapsid groups,

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

s and

burnetiamorphs Burnetiamorpha is a clade of biarmosuchian therapsids. Burnetiamorphs are the most derived biarmosuchians. The name Burnetiamorpha has been in use since South African paleontologist Robert Broom erected the group in 1923, but it has recently be ...

in particular. This indicated there had been an extensive dispersal of coeval therapsid groups between continents. They cautioned that the

paleobiogeography Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

animals (ancestrally four-limbed

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s) during the Permian remained poorly understood, with the expected dispersal abilities of various therapsid groups often differing from what can be seen in the fossil record and suggested more research was needed. Kammerer and Masyutin noted that while ''Viatkogorgon'' and ''Nochnitsa'' added to gorgonopsian diversity of the Kotelnich fauna, the group remained less rich in species than the therocephalians there. The low diversity and small size of the gorgonopsians there indicated that the assemblage of therapids was similar to that seen in the ''Pristerognathus'' Assemblage Zone in the

Karoo Basin The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a per ...

, South Africa, prior to the main round of gorgonopsian diversification there. In this regard, they found the basal position of ''Nochnitsa'' and ''Viatkogorgon'' intriguing, though they did not find it indicative of the Kotelnich locality being of an earlier age than the middle Permian South African strata that bear gorgonopsian fossils, based on the other kinds of therapid groups found among those faunas. They stated that while the "Russian clade" of gorgonopsians had probably diverged by the time the Kotelnich fauna existed, the absence of that clade in this locality suggests it had not yet undergone substantial diversification in Russia, and only became the dominant group of therapsid predators in the region later.

Paleobiology

Tatarinov noted in 1999 that ''Viatkogorgon'' could have pressed food against the concave, smooth palatine areas between the palatal teeth with its tongue. Palatal teeth are thought to have helped early synapsids and other basal

amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...

s (ancestrally land-dwelling vertebrates) grip food; these were lost in mammals which developed

secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves med ...

s instead. In 2018, Kammerer and Masyutin considered the sclerotic ring of ''Viatkogorgon'' remarkably large in proportion to its large eye socket, falling well within what would be considered

scotopic vision In the study of visual perception, scotopic vision (or scotopia) is the vision of the eye under low-light conditions. The term comes from the Greek ''skotos'', meaning 'darkness', and ''-opia'', meaning 'a condition of sight'. In the human eye, c ...

(ability to see in darkness) in therapsids, which suggests

habits. The Russian paleontologist Valeriy K. Golubev examined assemblages of Permian land vertebrates in Eastern Europe in 1999. He noted that ''Viatkogorgon'' and the therocephalian ''

Viatkosuchus ''Viatkosuchus'' is an extinct genus of therocephalians known from the Late Capitanian–Wuchiapingian Deltavjatia Assemblage Zone. See also * List of therapsids This list of therapsids is an attempt to create a comprehensive listing of all ...

'', the largest predators of the Kotelnich Subassemblage, were relatively small, not much different in size from the smaller predators of their assemblage, such as the therocephalians ''

Scalopodon ''Scalopodon'' is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The type species ''Scalopodon tenuisfrons'' was named in 1999 from the Kotelnichsky District of Kirov Oblast. ''Scalopodon'' is known from a singl ...

'', '' Scalopodontes'' and ''Kotelcephalon''. In 2019, the Russian paleontologists Yulia A. Suchkova and Golubev stated that the therocephalian ''

Gorynychus ''Gorynychus'' is a genus of therocephalian from the mid-Permian from Kotelnich, Russia. The genus contains two species, ''G. masyutinae'' and ''G. sundyrensis''. It was named after the three-headed dragon Zmey Gorynych (Змей Горыны� ...

'' from Kotelnich would have shared its niche as a dominant predator with ''Viatkogorgon''. The

paleoartist Paleoart (also spelled palaeoart, paleo-art, or paleo art) is any original artistic work that attempts to depict prehistoric life according to scientific evidence.#Anson, Ansón, Fernández & Ramos (2015) pp. 28–34. Works of paleoart may be r ...

and writer Mauricio Antón provided an overview of gorgonopsian biology in a 2013 book, writing that despite their differences from saber-toothed mammals, many features of their skeletons indicated they were not sluggish reptiles but active predators. While their brains were relatively smaller than those of mammals, and their sideways placed eyes provided limited

stereoscopic vision Binocular vision is seeing with two eyes, which increases the size of the visual field. If the visual fields of the two eyes overlap, binocular depth can be seen. This allows objects to be recognized more quickly, camouflage to be detected, spa ...

, they had well-developed turbinals in their nasal cavity, a feature associated with an advanced sense of smell, which would have helped them track prey and

carrion Carrion (), also known as a carcass, is the decaying flesh of dead animals. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...

. The canine saber teeth were used for delivering the slashing killing-bite, while the incisors, which formed an arch in front of the saber teeth, held the prey and cut the flesh while feeding. To allow them to increase their gape when biting, gorgonopsians had several bones in their mandibles that could move in relation to each other and had a double articulation with the skull—unlike in mammals where the rear joint articular bone has become the

malleus The ''malleus'', or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibra ...

ear bone. Antón envisioned gorgonopsians would hunt by leaving their cover when prey was close enough, and use their relatively greater speed to pounce quickly on it, grab it with their forelimbs, and bite any part of the body that would fit in their jaws. Such a bite would cause a large loss of blood, but the predator would continue to try to bite vulnerable parts of the body.

Motion

In 2004, Tatarinov interpreted the behavior of ''Viatkogorgon'' based on its skeletal features, which, while being generally similar to those of other gorgonopsians, had certain features that are unique or poorly understood. These concerned features of the locomotor apparatus in particular, which indicated a stage of swimming adaptations, while other features were consistent with those commonly seen in its group. Like other gorgonopsians, it had a long lumbar region of the vertebrae, of which the hindmost vertebrae showed an increased capability for vertical curvature, which was also the case for the neck vertebrae and, unusually, the hind part of the tail region. The presence of well-developed gastralia was one of its most unusual features among theriodonts, as were the hypapophyses of the tail region. In addition, the broad and somewhat shortened foot with unusual intermetatarsal contacts, which restricted the mobility of its individual digits, indicated transformation of the foot into a

-like structure. Tatarinov hypothesized these features to be adaptations for swimming; while ''Viatkogorgon'' was not a specialized aquatic predator, Tatarinov suggested its tail and feet enabled it to swim better than most other gorgonopsians. In particular, he thought the hind part of the tail was probably used for swimming, as is the case with reptiles with long tails that have hypapohyses, like ''

Mosasaurus ''Mosasaurus'' (; "lizard of the Meuse (river), Meuse River") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic Squamata, squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian an ...

''. Tatarinov noted that since the claw on the hindlimb's fifth digit was hooked and somewhat lengthened, it could have been used for protection and grooming, as in modern

monotreme Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...

s. The first digit could have had this function to a lesser degree, as it was free from contacting foot bones. The forelimb of ''Viatkogorgon'' was less specialized and could have performed more universal functions, as it lacked contacts between the digits. Antón stated in 2013 that while the post-cranial skeletons of gorgonopsians were basically reptilian, their stance was far more upright than in more primitive synapsids, like

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...

s, which were more sprawling. Regular locomotion of gorgonopsians would have been similar to the "high walks" seen in

crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...

ns, wherein the belly is carried above the ground, with the feet pointing forwards, and the limbs carried under the trunk instead of to the sides. The forelimbs had a more horizontal posture than the hindlimbs, with the elbows pointing outwards during movement, but the gait of the hindlimbs would have resembled that of mammals. As in reptiles, the tail muscles (such as the

caudofemoralis The caudofemoralis (from the Latin ''cauda'', tail and ''femur'', thighbone) is a muscle found in the pelvic limb of mostly all animals possessing a tail. It is thus found in nearly all tetrapods. Location The caudofemoralis spans plesiomorphica ...

) were important in flexion of the hindlimb, whereas the tails of mammals are merely for balance. Their feet were probably

plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...

(where the soles were placed flat on the ground), though they were likely more swift and agile than their prey. Their feet were more symmetrical compared to the reptilian condition, making contact with the ground more efficient, similar to running mammals.

Paleoenvironment

''Viatkogorgon'' is known from the Kotelnich locality, which consists of a series of Permian red bed exposures along the banks of the Vyatka River in Russia. It is specifically from the Vanyushonki Member, which is the oldest rock unit in the Kotelnich succession, consisting of pale or brown

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s (

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

and

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

s, with some fine-grained sand) as well as gray mudstone, and dark red mudstone at the base of this exposure. These mudstones were possibly deposited from suspension in standing water bodies on floodplains or shallow ephemeral lakes, that remained flooded for short periods of time, but the exact environment has not yet been determined, due to the lack of a primary structure of the

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s. The abundance of fossil rootlets and large

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

s indicates the landscape represented by the Vanyushonki Member was relatively humid and well-vegetated. The Kotelnich faunal complex was possibly coeval (of the same age) with the ''Pristerognathus'' Assemblage Zone of South Africa, which dates to either the latest

Guadalupian The Guadalupian is the second and middle Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico an ...

epoch of the middle Permian 260.26 million years ago, or the early late Permian. The Vanyushonki Member is the source of most of the tetrapod fossils from the Kotelnich locality, with skeletal remains being abundant here, often consisting of complete, articulated skeletons. Apart from the gorgonopsians ''Viatkogorgon'' and ''Nochnitsa'', therapsids from the locality include the

anomodont Anomodontia is an extinct group of non-mammalian therapsids from the Permian and Triassic periods. By far the most speciose group are the dicynodonts, a clade of beaked, tusked herbivores. Anomodonts were very diverse during the Middle Pe ...

Suminia ''Suminia'' is an extinct genus of basal anomodont that lived during the Tatarian age of the late Permian, spanning approximately from 268–252 Ma.Rybczynski N. 2000. Cranial anatomy and phylogenetic position of Suminia getmanovi, a basal anomod ...

'' and the therocephalians ''

Chlynovia ''Chlynovia'' is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The type species is ''C. serridentatus'', named in 2000. ''Chlynovia'' was originally classified within Scaloposauria, a group of therocephalians c ...

'', ''Gorynychus'', '' Karenites'', '' Perplexisaurus'', ''Scalopodon'', ''Scalopodontes'', and ''Viatkosuchus''. The

pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Per ...

Deltavjatia ''Deltavjatia'' is an extinct species of pareiasauromorph procolophonoid from the Tatarian stage of the Permian time period. It had a large body of about in length. ''Deltavjatia'' was an herbivore and lived in what is now Russia. The first sp ...

'' is particularly abundant there, and the

parareptile Parareptilia ("near-reptiles") is an extinct group of Basal (phylogenetics), basal Sauropsida, sauropsids ("Reptile, reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds ...

Emeroleter ''Emeroleter'' is an extinct genus of nycteroleterid parareptile known from the early Late Permian of European Russia. It was a long-legged lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to ...

'' is present. Fossil

ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant) have been identified,Brandão, S.N.; Antonietto, L.S; Nery, D.G.; Santos, S.G.; Karano ...

, root traces, and tree stumps have also been found.

References

Bibliography

* {{Taxonbar, from=Q1977932 Gorgonopsia Prehistoric therapsid genera Lopingian synapsids of Europe Permian Russia Fossils of Russia Fossil taxa described in 1999